I don't see why you couldn't do that. There is a deeds release fee (I don't remember exactly what it is called) but that is usually less than €50, and I'm sure AIB would get in touch with you about it in due course.
Remember that overpaying your mortgage/reducing your balance may not be the best use of your money. Your priorities should usually be:
- Paying off expensive debt (credit cards, personal loans, car loans, etc.)
- Building up an emergency fund in a savings/current account (3 to 6 months' living expenses)
- Saving money for any expenses you will have over the next few years (kids; childcare; adult children going to college, etc.)
- Maxing out your pension contributions (very large tax relief is given)
- Overpaying your mortgage